The invention concerns liquid dispensing valves, and in particular a valve for dispensing liquid glue accurately and at high repetition rate.
Liquid dispensing valves with reciprocal valve pins operating against an orifice with a valve closure seat are well known. Typically such valves are retracted by a solenoid and urged toward closure by a spring. See, as examples, U.S. Pat. Nos. 5,875,922, 5,405,050, and 4,962,871. See also copending application Ser. No. 09/075,776, filed May 11, 1998, now U.S. Pat. No. 6,032,832, which shows a pressure-balanced glue dispensing valve requiring only a very small spring pressure for valve closure.
It is among of the objects of this invention to simplify the design and structure of a liquid dispensing valve while making the valve structure more rugged, reliable and long-lasting, particularly in a high repetition rate glue head for applying glue to paper or other materials in a production line. This is accomplished through use of a novel device that isolates glue or other liquid from leakage up the shank of a valve pin while also applying the requisite spring force to maintain the valve closed under a range of specified pressure conditions.